It will take several days for them to turn into oldies. I've never had oldies on my V5 before, just V1-V4. I'm not sure if it'll change at age 7-10 like the V4. Just be patient and make sure you REJECT the matchmaker.
Also....if both your tamagotchi are a boy and a girl...if you mate them while they're oldies, you'll get the secret character, Oyajitchi, who evolves from baby to adult in an hour. =)